Fuel Flow at Full Power

[MikeOH]

My engine monitor (Insight G3) is showing just a bit over 16 gph at takeoff.  This seems a little low; I am told more like 18 gph.  If so, how is that adjusted on the M20F fuel injection system (I think it's a Bendix/RSA)?

Thanks!

[Bartman]

I see over 18 on takeoff in my J with A3B6D engine. I'm thinking it's about 18.6 gal/hr

[ThorFlight]

Same for my J. Right around 18 give or take a few tenths. Mostly give.


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[INA201]

I see 16 in my J full power boost pump on, a3b6d. Temps look good.

[carusoam]

That number is printed on the official M20 FAA document... (what’s that doc called?)

For the 310hp IO550 the number is restated/updated in the STC....

Roughly the max FF is generally twice the cruise FF....

If you aren’t getting enough FF the cylinders are going to show high CHTs.... during Take off and climb...

Sorry for the lack of detail....

Best regards,

-a-

[jaylw314]

37 minutes ago, MikeOH said:

My engine monitor (Insight G3) is showing just a bit over 16 gph at takeoff.  This seems a little low; I am told more like 18 gph.  If so, how is that adjusted on the M20F fuel injection system (I think it's a Bendix/RSA)?

Thanks!

There was a recent thread about fuel flow.  FWIW, my FF at full power is 16.9 gph or so, and people seem to run between 16 and 18 gph.  Check your FF meter k-factor, that might be off by a few percent, but realize the (non-idle) fuel flow in an IO-360 (Bendix RSA injection) cannot be adjusted.

[MikeOH]

16 minutes ago, carusoam said:

That number is printed on the official M20 FAA document... (what’s that doc called?)

For the 310hp IO550 the number is restated/updated in the STC....

Roughly the max FF is generally twice the cruise FF....

If you aren’t getting enough FF the cylinders are going to show high CHTs.... during Take off and climb...

Sorry for the lack of detail....

Best regards,

-a-

Yep... I see high temps during take-off and climb!  Usually have to back off the prop and I'm already climbing at 120.  I suspected low fuel flow might well be the issue.

[MikeOH]

3 minutes ago, jaylw314 said:

There was a recent thread about fuel flow.  FWIW, my FF at full power is 16.9 gph or so, and people seem to run between 16 and 18 gph.  Check your FF meter k-factor, that might be off by a few percent, but realize the (non-idle) fuel flow in an IO-360 (Bendix RSA injection) cannot be adjusted.

Uh, then how do I up the fuel flow to where it should be if the injection system cannot be adjusted?!?!?

[jaylw314]

You can't.

On the other hand, your fuel flow could be inaccurately low for a number of reasons, including if your k-factor on your FF meter is off.  If it's off by only 3%, that's about 0.5 gph off.  If you have a dirty air filter restricting your airflow, you could see low FF as well.

If your air and fuel flows are accurate, then all you can do is just watch your engine temps on takeoff.  If they are high, then check your baffling and cowls to improve your cooling.  If your temps are fine, just relax and live with it.

[Bartman]

Im not sure how much difference it would make, but if the prop governor is not allowing full rated 2700 RPM it might affect fuel flow. 

[carusoam]

See if @M20Doc has any quick ideas to cover the issues related to IO360 max FF and it’s adjustment (if any)

1) FF may actually be that low...

2) FF gauge may be telling a lie...  (check the calibration vs actual fuel burned)

3) something may need some cleaning if something is blocking the flow... or adjusting the flow improperly...

Best regards,

-a-

 

[Guest]

The RSA fuel injection servo only has 2 field adjustments, idle speed and idle mixture.  Maximum power fuel flow can only be changed at a shop with a flow test bench.

Clarence

[MikeOH]

Well, I make full rpm at take-off.

FF is likely pretty close as I have the K-factor dialed in to 1% error or less based on full top-off fuel fills.

The idea that something is blocking flow is worth checking! Thanks.

[MikeOH]

3 minutes ago, M20Doc said:

The RSA fuel injection servo only has 2 field adjustments, idle speed and idle mixture.  Maximum power fuel flow can only be changed at a shop with a flow test bench.

Clarence

Aha!

That makes sense.  I wonder what it would cost to pull the FI servo and have it flow-bench tested/adjusted?

[ArtVandelay]

That number is printed on the official M20 FAA document... (what’s that doc called?)

It’s not in the TCDS if that’s what you were thinking.

FWIW, according to Lycoming manual, 16gph at 2700 RPMs is the desired fuel flow at 200 HP (best power).

[Bob_Belville]

5 hours ago, teejayevans said:

It’s not in the TCDS if that’s what you were thinking.

FWIW, according to Lycoming manual, 16gph at 2700 RPMs is the desired fuel flow at 200 HP (best power).

But, is "best power" what we want to see on take off roll or do we want extra cooling fuel while near 100% power?

Per JPI data, I momentarily hit 18.2 gph departing OSH yesterday: 2706 max rpm, 29.2 max MP,  93% power, 790 field elevation. IO360 A1A

[Bob - S50]

11 hours ago, MikeOH said:

Yep... I see high temps during take-off and climb!  Usually have to back off the prop and I'm already climbing at 120.  I suspected low fuel flow might well be the issue.

A bit off track, and see if others agree, but if you CHT's are high, don't reduce RPM, that will most likely make it worse.  If you want to reduce power because everything is hot, and assuming you are still full rich, do it with the throttle.

[1964-M20E]

11 hours ago, MikeOH said:

Uh, then how do I up the fuel flow to where it should be if the injection system cannot be adjusted?!?!?

The fuel flow on the servo at full throttle may not be adjustable but you can ensure that when the red knob is pushed all the way in the mixture lever on the servo is in the full rich position.  This is linkage adjustable.

[Hank]

6 hours ago, teejayevans said:

It’s not in the TCDS if that’s what you were thinking.

FWIW, according to Lycoming manual, 16gph at 2700 RPMs is the desired fuel flow at 200 HP (best power).

My O-360 Owners Manual shows 18.2 gph at sea level to produce full power, and that's only 180 hp. Full rich, 2700 too. Surely 200 hp needs more fuel?

[Browncbr1]

Last month, I cleaned the finger screen at the fuel servo and found a slight increase in FF on takeoff... (a little bit of debris was found)   caveat; I also replaced the mixture cable, so it could have been that previous cable wasn't hitting the stop all the way.

[ArtVandelay]

But, is "best power" what we want to see on take off roll or do we want extra cooling fuel while near 100% power?
Per JPI data, I momentarily hit 18.2 gph departing OSH yesterday: 2706 max rpm, 29.2 max MP,  93% power, 790 field elevation. IO360 A1A

Do you need the extra cooling? My J stays below 375° with similar numbers, closer to 17 gph.

[ArtVandelay]

My O-360 Owners Manual shows 18.2 gph at sea level to produce full power, and that's only 180 hp. Full rich, 2700 too. Surely 200 hp needs more fuel?

Not if it’s more efficient, the 180 is sending a few gph out the exhaust in unburned fuel.

[Marauder]

8 hours ago, teejayevans said:

It’s not in the TCDS if that’s what you were thinking.

FWIW, according to Lycoming manual, 16gph at 2700 RPMs is the desired fuel flow at 200 HP (best power).

That is where mine has historically run:

2016

 

2017

 

2018

[jaylw314]

12 hours ago, MikeOH said:

Aha!

That makes sense.  I wonder what it would cost to pull the FI servo and have it flow-bench tested/adjusted?

I'd check the air filter and intake first!!

[carusoam]

Thanks TJ,  TCDS is the document I was thinking of....

From IO550 Experience...

Max Power Using the EGT method comes in a range from 200°F to 300°F ROP... (calibrated gauge on the instrument panel, blue box method...)

This is engine specific, but can be extended to other NA engines...

As for CHT data... it would be wise to specify the ignition timing that you are using while comparing these data points... or if you have changed the CR at all.... As one of us has done recently...  (firewall forward STC thread...)

Some IO360s Are Set To 20° And Others have been Set to 25° BTDC...

The IO550 is Set to 22° BTDC....

The further BTDC... the more fuel is converted to power... the cost is heat generated inside the cylinders... and increased risk, decreased safety margin, of piston melting ping...

It would be great to change timing in cruise to something like 30° BTDC under low power conditions... (Thinking out loud after seeing electronic ignitions this week)

Ordinary PP thoughts only, not a mechanic...

Best regards,

-a-